This was a weird one, and I’m not sure how I feel about it. See, Mary not quite Shelley and Percy Shelley and Mary’s sister (I think) and Lord Byron are all hanging out at Byron’s place, just like we saw in a recentish episode of Doctor Who. And they made a bet to write a scary story, which as we all know was the genesis of a certain Modern Prometheus. Fine so far.
Only Mary also had a miscarriage, and started getting obsessed with this idea she had for a book, and Percy is getting more and more grossed out by her whole vibe, and meanwhile she’s got Victor Frankenstein (who is just Percy except dressed in black and nobody else can see him) stalking and/or courting her, and basically the whole movie is this obsession she has with her book, or maybe the book is haunting her? I was at first really unhappy because it seemed like they were saying she was being externally haunted and the book was being given to her, which is kind of a bullshit take. But I’m pretty sure it’s the obsession or maybe haunted by the book as she goes[1] but at least she’s really the one writing it angle instead, and that’s alright.
I did a shallow dive into the history of a handful of characters afterward, and while they are certainly taking some liberties here, the movie was in the end at least a reasonable fiction of how it might have happened. (But it definitely did not happen this way, all the same. Also, not for nothing, Percy Shelley, good poet though he might be, was kind of crap at being a man.)
[1] A Nightmare Wakes kind of implies the latter haunted version, but only kind of.